1. Field of the Invention
The present invention generally relates to a liquid delivery tube, and more particularly, to a catheter for delivering medication to a patient, the catheter being constructed from micro-bore tubing attached to a needle. The needle is attached to the external surface of the tubing so that it does not restrict the flow of fluid through the tubing. The tubing has a uniform internal diameter along its entire length. When used to deliver, under a fixed pressure, a liquid medication of a known viscosity the flow rate of the liquid can be closely controlled by cutting the microbore tubing to a desired predetermined length
2. Description of the Prior Art
It is well known in the industry that the flow rate of a fluid from an infusion device can be controlled by a flow restricting orifice, tube, or micro-passage of various configurations. There are several common embodiments of this art in commercial use today. U.S. Pat. No. 3,951,147 to Tucher, et al, describes several flow restrictors including a long stainless steel tube which is wound around the infusion pump body, a long spiral groove formed by inserting a threaded wire into a tube, and other similar configurations.
U.S. Pat. No. 4,386,929 to Peery, et al, discusses a short capillary tube contained within the pump housing for regulating the flow rate of medication dispensed. He also mentions other types of flow restrictors such as porous plugs, fiber bundles, and porous films, all of which are contained within the pump housing.
The devices described in Tucher et al and Perry et al all suffer from the disadvantage that in order to change the flow rate, a different pump must be used. This creates an inventory problem for users who wish to utilize a specific flow rate at the time of application of the infusion pump. In addition, these infusion pumps generally do not provide the capability of delivering fluid to more than one catheter at a time since each catheter would require its own flow restrictor to insure a proper flow rate through the catheter.
U.S. Pat. No. 3,094,124 to Birtwell discloses a large bore arterial having a tapered tip with a small diameter opening. The tapered tip is marked in intervals to assist a user in cutting the catheter to a desired outer diameter to match the diameter of a severed arterial into which it is to be inserted for recirculation of blood during an open heart procedure. In the Birtwell devices the flow through his catheter is controlled by the diameter of the outlet opening or a attachable stainless steel cannula inserted in that opening. The internal diameter of the remainder of the catheter is not taken into consideration and flow is not controlled by severing a predetermined length of the catheter. Instead, flow is controlled by varying the size of the end of the tapered portion of the catheter.
U.S. Pat. No. 4,741,733 to Winchell, et al, discloses a flow restrictor placed external to the pump body in the delivery tube system. This system can be used where multiple catheters are required to adequately infuse medication into the body. The flow restrictor disclosed consists of a short restrictor tube, usually a glass micro-bore tube, contained within a plastic housing.
In current practice, the flow restrictor housing can be removed from the infusion device delivery system, branching connectors added, and flow restrictors, each optionally having different flow rates, added to the infusion system. In this way, multiple catheters having different flow rates can be achieved. However, it is still necessary that an inventory of flow restrictors having different flow rates be maintained so the user can select from a variety of flow rates at the time of application of the infusion device.
In order to overcome the need to maintain an inventory of catheters having different flow rates, it would be desirable to have a catheter whose flow rate could be easily adjust at the time of use. Such a catheter would enable only one catheter to be inventoried yet allow the user to adjust the flow through the catheter to any flow rate desired at the time of use.
Accordingly, the objects of the current invention are to provide a new and improved catheter for dispensing fluids and medications from an infusion device, the improved catheter having a lumen through its length providing flow restriction along the entire length of the catheter tubing such that the flow rate can be adjusted at the time of use. In a preferred embodiment the internal diameter of the tubing (i.e., the lumen diameter) is closely controlled to be a consistently uniform along its full length. Such tubing may be referred to as a calibrated flow, microbore tubing.
In accordance with these and many other objects of the current invention, a catheter tube embodying flow restriction along its entire length can have its flow rate adjusted by trimming the length of the flow restricting catheter tube. The tubing could be trimmed at the time of manufacture or could be trimmed at a later time of use. Length markings to aid in trimming the catheter tubing could be placed on the outside of the catheter with ink, laser ablation, or other suitable method of marking.
The flow restricting catheter tubing can be any flexible micro-bore tubing that can be easily trimmed without distorting the trimmed end. The catheter tubing is attached to the elastomeric septum of the infusion device by a needle which is adhered to one end of the catheter tubing.
As the flow restricting catheter tubing is shortened by trimming, the flow rate will increase in linear proportion to the decrease in initial length of the catheter tubing. If the tubing is cut in half, the flow rate will double.